In vehicle systems, numerous sensors are employed to monitor operating parameters such as current, speed, angle, linear position, rotational direction, temperature, etc. of an article associated with a control module, such as a power steering module, a fuel injection module, an anti-lock brake module, etc. The sensor output signals are provided over a communication bus to a system controller, such as an Electronic/Engine Control Unit (ECU) or Engine Control Module (ECM), which processes data provided by the various sensors. Vehicle systems commonly employ communication buses that are coupled to multiple sensors (and/or other devices) to communicate commands and data (e.g., a shared bus network).
Commonly, vehicle system components that are considered safety critical, such as the various ECUs and ECM, might employ relatively faster, more complex and more expensive buses, such as CAN (Controller Area Network) or FlexRay™ buses. For example, the ECM might employ a CAN bus to communicate with sensors in critical systems such as the transmission system, braking system, airbag control system, traction/stability control system, and other similar systems. Higher bandwidth automotive components, such as multimedia, entertainment and location-based systems might employ Bluetooth® (IEEE 802.15), MOST (Media Oriented Systems Transport), FireWire (IEEE 1394) or other similar communication links that are also relatively fast, complex, and expensive.
The LIN (Local Interconnect Network) protocol is a single wire bidirectional serial communication protocol commonly used to communicate between relatively lower bandwidth and relatively less safety critical devices in the vehicle system. A communication bus operating in accordance with the LIN protocol links a master device (e.g., the ECM) and up to 16 slave devices. The LIN protocol can be implemented having a relatively simple and cost effective transceiver circuit due to its lower bandwidth and single wire serial communication. Therefore, less data intensive and less safety critical automotive subsystems might beneficially employ a LIN bus to reduce complexity and cost, for example, seat controls, window controls, climate controls, windshield wiper controls, lighting controls and other similar systems.
The communication protocol, features, and hardware and software requirements of the LIN protocol are set forth in the LIN Specification Package (hereinafter “LIN specification”), published by the LIN Consortium, Revision 2.2A, on Dec. 31, 2010, which is hereby incorporated by reference herein in its entirety. As described in the LIN specification, the bus derives its power from the automobile battery voltage (Vbatt) and ground (or circuit common) of the automobile electrical system. The LIN specification also sets forth a minimum threshold voltage for a receiver to detect a logic high signal (THRec), a maximum threshold for a receiver to detect a logic low signal (THDom), duty cycles for transmitted bits, and rise and fall times for logic transitions.
However, shifts in supply voltage (for example based on the charge state and operating condition of the vehicle battery), resistance and parasitic components (i.e., inductance and capacitance) of bus cables, and electromagnetic interference (EMI) present on the bus can make it difficult for LIN transmitters to meet the LIN protocol requirements. For example, a long bus cable might have relatively high resistance and parasitic components, and be exposed to relatively high amounts of EMI. Thus, a LIN transmitter coupled to a long bus cable might have difficulty meeting the timing requirements for logic state transitions to charge or discharge the bus for a logic high or logic low, respectively, to be detected by a LIN receiver. Similarly, a short bus cable might have relatively low resistance and parasitic components, and be exposed to less EMI. Thus, a LIN transmitter coupled to a short cable might operate inefficiently from a power perspective since the transmitter might be driving the bus at a higher current draw than necessary (e.g., greater power consumption). Further, by having very quick logic state transitions, a LIN transmitter might generate additional EMI for other components coupled to, or located in proximity to, the bus. Therefore, an improved transmit driver is envisioned for LIN devices to communicate more reliably and with higher power efficiency.